Various types of detection devices have been developed for obtaining various data of a fluid by passing an objective fluid through a detection flow channel in the device. The detection devices include electrical detection devices for measuring the concentration or temperature of an objective substance in a fluid, and optical detection devices for measuring the concentration of an objective substance in a fluid. Known optical detection devices include concentration detection devices which introduce detecting light from a light source into a fluid, measure a quantity of transmitted light, and calculate the concentration; and devices which measure the concentration and temperature of an objective substance from light concentration or light divergence by a lens effect. In such devices, generally, a laser beam of about 1 mm diameter is allowed to penetrate through a flowing liquid in a flow channel of about 10 cm long and about 5 mm wide, and refractive index distribution in the sectional radial direction of the circular tube is derived by detecting the focusing point to measure the concentration of an objective substance in the fluid. For detection of the focusing point of the light beam or the maximum light intensity position, the beam diameter or the light intensity is measured by a photodiode (PD) or a measuring instrument called generally a beam analyzer.
Japanese Patent 2747933 discloses a concentration measurement method conducted as shown below. A catalyst immobilized on an outer wall of a tubular member catalyzes a reaction of a substrate substance to be detected in a fluid to cause heat generation or heat absorption. Consequently, the medium within the tubular member is heated or cooled by the wall of the tubular member to cause expansion or constriction and to cause a nonuniform density distribution from the center toward the outer wall in the tube, resulting in a nonuniform refractive index distribution. Upon introduction of detecting light into the medium, the light beam is deflected owing to the nonuniform refractive index distribution and is focused at a certain position. The refractive index distribution is determined from the focus position of the detecting light to show the heated or cooled state of the medium. This heated or cooled state shows the degree of the reaction of the substrate on the outer wall. From this, the concentration of the substrate is determined.
Japanese Patent 2691374 discloses a concentration measurement method conducted as below. An objective substrate in a fluid having been introduced into an outer frame is allowed to penetrate a porous wall of a tube constituted of a porous material to dissolve and diffuse into the medium in the tube. Thereby, the substrate concentration changes gradually toward the axis of the tube. Upon introduction of detecting light from one end of the tube, the light is converged toward the center of the tube, or is diverged outward from the center. By receiving this detecting light, change of the beam diameter, energy density, or converged point is measured, and therefrom the refractive index distribution is measured. From the refractive index distribution, the substrate concentration distribution in the medium is derived, and further the concentration of the substrate in the detection-objective fluid in the outer frame is estimated.
In recent years, micro total analysis systems (μ-TAS) have been developed which conduct detection or measurement in a small scale to decrease the quantity of an examination sample, to reduce the cost, or to simplify the operation. This μ-TAS is a system which utilizes fine flow channel formed on a chip in a size of from several millimeters to several centimeters by a technique of MEMS (microelectro-mechanical system) or the like and conducts various examination of measurement in the flow channel.
However, it is difficult to utilize the μ-TAS in the optical detection method employing conventional device constituted usually of a flow channel of about 10 cm long and 5 mm wide because of liability to insufficiency of measurement accuracy and response speed. In other words, the complicated constitution employed in the conventional detection device hinders realization of high integration, the feature of the μ-TAS.
Electrical measurement by the μ-TAS, for example, is liable to be affected by an electric noise, resulting in a low measurement accuracy. Absorption measurement by the μ-TAS, at a high concentration of the detection-objective substance in the examined fluid, is conducted optically with very small quantity of the light for the signal generation owing to light absorption to give a low S/N ratio (signal to noise ratio). On the other hand, with an examination-objective fluid diluted to avoid the drop of the S/N ratio, the signal itself becomes weak to retard difficult the measurement with a high S/N ratio. Measurement by optical focus detection employs necessarily a beam analyzer in a large size of tens of centimeters, which is not suitable for the μ-TAS. Detection with a simple PD conducts detection of light intensity at plural positions by moving the PD along the beam, which makes complicated the constitution to hinder miniaturization and high degree of integration even with the μ-TAS.
In the inventions of Japanese Patents 2747993 and 2691374, the tube constituted of alumina or the like employed necessarily for the invention should be precise in the shape and dimension not to affect adversely the light refractivity and converging position. Such a tube cannot readily be prepared, and will be of a high production cost, and may makes troublesome the handling and operation.